1980 6-71 TI JT galloping

Having an issue with my starboard engine. At start up it will gallop 3-5 times, not a lot of smoke. This is not the issue. The galloping stops, the smoke stops, engine sounds and feels excellent. Idles at 596-600 rpm. When the temp reaches about 130, according to the temp gauge, engine rpms fall off and stalls. I can restart it immediately and keep it running by increasing the throttle control to about 1000 rpm. The engine will gallop and stall if I try and let it idle. I can mess with the throttle, and finally get it to idle. It will go into gear and run fine until I put it back into neutral, then she will gallop once and stall????? Very irritating trying to maneuver at the dock. Any experience with this?

Two days ago I replaced the spring at the idle speed end of the governor, also found two thick shims and two thin shims, installed the two thick shims and four thin shims, rechecked the rack, readjusted the idle and reset the buffer. Engine ran great the rest of the day no issues whatsoever. Started the engine two days later and the problem was back. Looking for a direction. Any suggestions?